1. Field of the Invention
The present invention is related to a device for accessing address information in an optical disc and, more particularly, to an address-accessing device that is capable of adjusting the decision level and phase offset when receiving the address signals.
2. Description of Related Art
Optical discs, such as digital versatile discs (DVDs) and video compact discs (VCDs), are already used extensively in business and personal activities. They are usually used to record mass data or video files, such as movies, music files or application software. Recently, in order to enlarge the storage capacity of optical discs, a novel standard related to Blu-ray discs, which have five times the storage capacity of DVDs, was developed to fulfill the consumers' needs in the future.
Reference is made to FIG. 1a, which is a schematic diagram of a conventional optical disc. Generally, in the manufacture of an optical disc, a spiral pre-groove 1 should be formed to define the physical addresses of the optical disc. Reference is made to FIG. 1b, which is an enlarged diagram of a segment of the pre-groove. The pre-groove segment 2 is formed in a specific wobbling manner, such as a specific phase or frequency, to define the physical addresses of the optical disc.
In general, after the fabrication of a Blu-ray disc is finished, the pro-groove of the Blu-ray disc must have multiple address words, called address-in-pregroove words (ADIP words) for definition of the physical addresses. Conventionally, every ADIP word of the Blu-ray disc has 83 address units, called address-in-pregroove units (ADIP units). Each of the ADIP units has 56 nominal-wobble-length units (NWL units).
Therein, every ADIP unit has minimum-shift-keying marks (MSK marks). The relative positions of the MSK marks are used to identify the attributes of the ADIP units. Furthermore, the physical addresses are found via identification of the digits (“1” or “0”) recorded in the ADIP words. Thus, the physical address of every location of the Blu-ray disc can be found by identifying and decoding the digits recorded in the ADIP words. Thereby, a Blu-ray optical drive can performs a Read or Write operation according to the information of these physical addresses.
In accordance with the specification of Blu-ray discs, the first eight ADIP units of an ADIP word are formed by combining sync units and monotone units, and the last 75 ADIP units are formed by combining data units and reference units. In addition, each one of the last 37 NWL units (i.e. NWL 18-55) in an ADIP unit, which has 56 NWL units in total, is formed in one of three predetermined structures.
Reference is made to FIGS. 2a and 2b, which show the predetermined structures. These predetermined structures are cos(wt), cos(wt)+sin(2 wt)/4 and cost(wt)−sin(2 wt)/4. Therein, “t” represents time and w=2pi*fw, where “fw” represents a predetermined frequency value for NWL units. The cos(wt)+sin(2 wt)/4 structure represents “1” and the cos(wt)−sin(2 wt)/4 structure represents “0”.
Reference is made to FIG. 3. In an ADIP word, the first eight ADIP units are formed by combining sync units and monotone units, and their NWL 18-55 are formed as the cos(wt) structure. The last 75 ADIP units of the ADIP word are divided into 15 groups. Each of the groups consists of one reference unit and four data units. Depending on the value of the digits (i.e. “1” or “0”), the data units are designated as data_1 or data_0. Each one of the NWL 18-55 for data_1 is formed as the cos(wt)+sin(2 wt)/4 structure and the same for data_0 is formed as the cos(wt)−sin(2 wt)/4 structure. Furthermore, each one of the NWL 18-55 in the reference unit is formed as the cos(wt)−sin(2 wt)/4 structure. This means that the NWL 18-55 of the reference unit has the same structure as that of the data_0 unit.
Reference is made to FIG. 4, which is a block diagram of a conventional address-accessing device. The device has a matching unit 403, a sum & sampling unit 405 and a decoder 407. The matching unit 403 is used for calculating a matched value of a matching signal (i.e. sin(2 wt)). The matching unit 403 is implemented by using a matched filter. The sum & sampling unit 405 is used to sum up the matched values of the NWL 18-55 of an ADIP unit to produce a reference value. The decoder 407 is used to determine the structure type of the NWL 18-55 of the ADIP unit according to the reference value. However, due to an unknown phase offset or a gain variation, the decoder 407 may have an unpredictable reference offset and make the error rate of the address access increase.
Aiming to solve the problem caused by the phase offset, another address-accessing device was proposed. Reference is made to FIG. 5, which is a block diagram for this kind of address-accessing device. This device has a matching unit 503, a sum & sampling unit 505, a decoder 507 and a phase-offset detector 509.
The matching unit 503 is used for calculating a matched value according to a matching signal (i.e. sin(2 wt+q)), in which “q” represents the phase offset. The phase-offset detector 509 is used to estimate the value of q according to the matched value and adjust the phase reference value of the matching unit 503. The sum & sampling unit 505 is used to sum up the matched values of the NWL 18-55 of an ADIP unit to produce a reference value. The decoder 507 is used to determine the structure type of the NWL 18-55 of the ADIP unit according to the reference value. However, this device needs a matching circuit whose phase reference value is adjustable. It makes the difficulty and complexity of the circuit design increase greatly.
Accordingly, as discussed above, the prior art still has some drawbacks that could be improved upon. The present invention aims to resolve the drawbacks of the prior art.